ming@smthelp.comThis article describes that paying attention to some details can often prevent common problems in assembly processes and equipment selection.

Question: Can I use a small spatula to remove misprinted solder paste from the board? Will this get the solder paste and small tin beads into the holes and small gaps?

Answer: Using a small spatula to remove the solder paste from the misprinted board may cause some problems. It is generally practicable to immerse the misprinted board in a compatible solvent, such as water with an additive, and then remove the small tin beads from the board with a soft brush. I prefer to soak and wash repeatedly instead of violent dry brush or shovel. After the solder paste is printed, the longer the operator waits to clean the misprint, the harder it is to remove the solder paste. Misprinted boards should be placed in the soaking solvent immediately after the problem is discovered, as the solder paste is easily removed before it is dried.

Avoid wiping with a strip of cloth to prevent solder paste and other contaminants from smearing on the surface of the board. After soaking, brushing with a gentle spray can often help remove unwanted tins. It is also recommended to dry with hot air. If a horizontal stencil cleaner is used, the side to be cleaned should face down to allow the solder paste to fall off the board.

As usual, note that some details can eliminate undesirable conditions, such as misprinting of the solder paste and removal of the solder paste from the board. It is our goal to deposit the right amount of solder paste at the desired location. Stained tools, dry solder paste, and misalignment of the stencils and plates can cause undesirable solder paste on the underside of the stencil or even the assembly. During the printing process, the template is wiped with a certain pattern between printing cycles. Ensure that the template is seated on the pad, not on the solder mask, to ensure a clean solder paste printing process. On-line, real-time solder paste inspection and inspection prior to reflow after component placement are process steps that reduce process defects prior to soldering.

For fine-pitch stencils, if damage is caused between pins due to thin stencil cross-section bending, it can cause solder paste to deposit between the pins, causing printing defects and/or short circuits. Low viscosity solder paste can also cause printing defects. For example, high operating temperatures or high blade speeds can reduce the stickiness of the solder paste during use, resulting in printing defects and bridging due to excessive solder paste deposition.

In general, the lack of adequate control of materials, solder paste deposition methods and equipment are the main causes of defects in the reflow soldering process.

Question: What type of assembly board depaneling equipment provides the best results?

Answer: There are several sub-board systems that offer a variety of techniques for slab assembly boards. As a rule, there are many factors that should be considered when selecting such a device. Regardless of whether there is routing, sawing or blanking to separate individual panels from the composite panel, stable support during the splitting process is the most important factor. Without support, the resulting stress can damage the substrate and solder joints. Distorting the plate, or stressing the assembly during the splitting, can result in hidden or significant defects. While sawing often provides minimal clearance, shearing or die cutting with tools can provide cleaner, more controlled results.

In order to avoid component damage, many assemblers attempt to maintain component solder joints at least 5.08 mm from the edge of the board when the splitter is required. Sensitive ceramic capacitors or diodes may require extra care and consideration.

This article explains and discusses the guiding principles governing 0201 placement in both high-volume and high-mix assembly operations.

By Ming Gan, ming@smthelp.com

Although generally considered to be a relatively recent development, printed circuit boards (PCBs) have been available since the early 1950s. Since then, the demand for smaller, lighter, and faster electronic products has driven electronic components, PCB, and assembly equipment technology toward SMT.
The earliest general acceptance of SMT occurred in the early 1980s, when machines such as the Dynapert MPS-500 and FUJI CP-2 entered the market. At that time, 1206 (3216) resistors and capacitors were the most popular placement components. However, in one or two years, 1206 gave way to 0805 (2125) as the most common component package for SMT placement.
During this time, both machines and components evolved rapidly. As the machine became faster and more flexible, the 0603 (1608) component began to evolve. At this point, many assembly machine manufacturers went back to the R&D, research and development lab to re-evaluate the technology used to accommodate these newer, smaller components. Higher resolution cameras and smaller vacuum nozzles are among the variations that these components bring to the assembly equipment.
The emergence of 0402 (1608) packaging poses further challenges in all aspects of PCB assembly. In terms of machine development, vacuum nozzles have become smaller and more fragile. A new focus is placed on the component’s feeder, which acts as a unit for improvement, giving the machine more accurate parts.
With the advent of 0402 components, process challenges have increased to those that need to be addressed for successful component placement. Solder paste printing becomes even more critical – stencil thickness and solder paste mesh are increasingly important process considerations. The technology required for such placement also involves significant new costs.
The combination of these factors creates a new form of packaging that is the slowest to adopt in the history of the electronics industry. In total, for almost five years, 0402 packaging was widely accepted in the industry – and many assembly plants today never put a 0402 sheet.
Now, I entered 0201.
Over the past year and a half, 0201 placement has been a key topic of discussion throughout the industry. Due to the size, weight and power consumption requirements, many OEM board assemblers need to incorporate even smaller components and technologies into their products. Contract manufacturers (CM, contract manufacturer) must also have new technologies to keep the assembly process up to date and provide customers with a complete range of services. For machine builders, the challenge is to develop more resistant to obsolete assembly equipment in an era of dynamic technological change.

0201 placement challenge
The placement of the 0201 component is more challenging than the component intervention in front of it. The main reason is that the 0201 package is approximately one-third of the corresponding 0402 size.
The previously acceptable machine placement accuracy immediately became a limitation of the introduction of 0201. In addition, the traditional industrial tapeding specification allows for too much movement for reliable 0201 placement, and the level of process control must be increased to make the 0201 placement a production reality.
Although these obstacles are very large, they are far from insurmountable. Of course, they need all the determination, because the technology necessary for the 0201 placement requires a lot of money and top management’s promise of research and development (R&D).

The key to reliable 0201 placement
At FUJI, the aggressive R&D program has produced the ability to make all circuit assembly machines compatible with 0201 at 100% speed, with a minimum suction reliability of 99.90%, a target suction reliability of 99.95%, and minimal placement reliability. It is 99.99%. In the beginning, every aspect of the design was evaluated for its ability to work on a complete 0201 program, and the combination of single elements of closely related machine component parameters proved critical to success. These parameters include:

Figure 1 Component feeder table. The R&D program concluded that the ability to precisely position the carriage table – and make minimal adjustments to compensate for the inaccuracy of the tape – is a key factor in achieving component pickup reliability above 99.95%.

To achieve this, the feeder table must be precision machined to ensure repeatable positioning of the individual feeders and combined with a high-resolution semi-closed-cycle servo system using a two-track linear moving guide. This design allows for minor adjustments – based on the results of the suction accuracy as judged by the vision system. This ensures that the component is as close as possible to the center.Component feeder. The feeder must be manufactured to extremely tight tolerances to ensure repeatability of the suction position, regardless of component height and a large number of possible component positions. The mechanism used to position and lock the feeder in position must be durable and precise, yet be user friendly. In addition, the materials used to make the feeder must be high in strength and light in weight to allow for ergonomic operation while ensuring precise, repeatable delivery of the carrier tape.The feeder drives the sprocket. The drive sprocket plays a key role in the ability of the machine to position the component tape. The shape, taper and length of the drive sprocket teeth significantly affect the ability of the feeder to position the tape. Other factors have also been investigated, such as the diameter of the drive sprocket and the number of belts in contact with the sprocket. Changes to the basic sprocket design resulted in improved positioning accuracy, with earlier designs increasing by 20% in the X direction and 50% in the Y direction.

Figure 2 sucks the head. After properly feeding the component, the next step is to draw the component onto the vacuum nozzle and bring it to the board. Vacuum nozzles are compliant to absorb shock during pick-and-place components, compensate for small variations in solder paste height, and reduce the risk of component breakage. For these reasons, the nozzle must be able to move within its fixture.

Material selection, material hardness, machining tolerances, and thermal characteristics must all be understood to construct a reliable suction head. The nozzle must move freely within its holder without sacrificing accuracy (Figure 1).The nozzle shaft is assembled. The nozzle shaft is also a key design element – eliminating overdrive by keeping the entire nozzle in direct alignment with the shaft assembly. Overpressure is caused by the inertia generated when the head is moved up and down. If the nozzle and the shaft are not in a straight line, there is a little whip – or overpressure. Overpressure causes a change in positioning accuracy, which is determined by the speed of movement, the weight of the nozzle, and the weight of the component. By eliminating overpressure, direct alignment reduces the number of negative factors associated with component pick-and-place placement (Figure 2).Figure 3 nozzle design. Variations in the design of the nozzle are an important factor in allowing the 0201 component to be received. In order to draw a 0.6×0.3 mm component, the nozzle must have an outer diameter of no more than 0.40 mm. This forms a long, thin nozzle shaft that is fragile but must also maintain precision to maintain high reliability of suction. Changes from the linear axis to the tapered design increase the nozzle strength and allow the nozzle to resist bending (Figure 3).Matrix structure. All machines generate vibrations during operation. The base frame design is a key first step in reducing the speed and motion effects of vibration and harmonic resonance. By using a cast iron base frame and state-of-the-art structural technology, vibration and harmonic resonance can be reduced to a controllable level within the machine, so that negative effects can be dealt with.Up to standardThrough all six key factors, the obstacles to reliable 0201 placement have been eliminated. As a result, R&D’s focus has shifted to newer, smaller components, and 0201 is no longer considered a leading edge component packaging technology.For 0201 component placement, the accepted process window is approximately 75 μm X and 75 μm Y at 3 。. To achieve 6 贴 placement reliability, the X and Y tolerances must be reduced to 50 μm. The latest high-speed placement equipment has a rating of 66μm with an actual standard deviation of approximately 35~45μm. As the 0201 component becomes more widely used and the manufacturing process becomes tighter, improved accuracy can be achieved.The difference in component size between suppliers poses a challenge to 0201 feeding and placement. Bulk feeding is being opened and should be available in 2001.Although the machine now has this capability, only a small percentage of users will be ready to take the 0201 placement in the next 12 to 24 months. This is similar to the introduction of a ball grid array (BGA) and 0402 components, in which the machine’s capabilities are ahead of the process state.

Challenge ahead
While the placement of 0201 components is now a standard feature of new placement equipment, additional work is needed to improve the overall process for the end user. The relationship between machine builders, component suppliers, board manufacturers, formwork factories, and solder paste manufacturers needs to be strengthened to create a more seamless development process. The end result will be a unified understanding of the process and a better working relationship that will benefit end users, especially by making new production technologies faster and more efficient.

SMT patch bulk material problems have plagued many SMT people, as we all know, once the placement machine starts, there will definitely be a problem in the SMT production line. For a variety of reasons, many bulk materials are produced, thrown, or are originally bulk materials, or other reasons. Some bulk materials, such as resistors, capacitors, inductors, etc., are not easily distinguishable and have little value in themselves, and there is no value for reuse. However, for large devices, especially some imported chip components, they are of high value and can be distinguished and distinguished, so they are generally reused. However, for scattered components, if the original package is a tray or a suitable tray, the problem may be solved better. Otherwise, it may be more difficult to handle. Southern Machinery today will talk about the handling of bulk material in the SMT production line. Method and process.First, the bulk material handle process

Bulk material: refers to the components that are separated from the original packaging during the production process due to machine throwing, or loading and unloading materials.

Third, job responsibilities

Material staff: responsible for the collection, classification, identification, storage, placement, and placement information of bulk materials, and the material loss rate is calculated according to the order.

QC in front of the furnace: responsible for the manual placement of bulk materials, the front back grain and material code confirmation, PCBA mark, and the classification of bulk materials.

QC after the furnace: It is responsible for checking and checking the first piece of all the machines, and the quality is abnormal. Immediate feedback is provided to the front station to improve and track.

Fourth, the work content

In the production process, the material may be thrown due to equipment and other factors, so the operator should check the material step before the patch and after the shift, and check the throwing box and the trash can each time the garbage is dumped. Collect the bulk material and report to the supervisor about excessive bulk material anomalies.

According to the shape of the components, the bulk material is classified according to the shape of the components, and the back code of the components is checked to determine the material code. Then, the checked bulk materials are packed in anti-static bulk box or bulk bag, and the material code identification is performed to confirm the signature of the person. .

When using machine mounting, the operator should first check whether the components are consistent with the normal materials, confirm the material number, and then load the FEEDER tape.

The first piece of material feeding / mid-way refueling, the technician firstly inspects the materials that will be short of materials in the machine half-hour in advance, and collects the materials of the same item number in the component preparation area, and check them correctly, and submit them to the quality department QC/materials. The staff will check again and confirm the total signature of the refueling sheet.

Use of PCB Pallets in Wave Soldering
Patch components are used more and more on the circuit board, but there are still some perforated components between them. For this kind of board, selective soldering is the best solution, but not every company has enough funds to purchase selective soldering equipment, or the number of this type of circuit board is too small, specifically to buy selective soldering equipment is not Cost-effective. Manual welding is prohibited in certain industries such as the automotive industry

Therefore, in PCB wave soldering, using trays to block those patch components is a good method: reliable, fast production, and adaptability to high-capacity requirements.

The benefits of using trays:
Lead-free soldering requires higher soldering temperatures. Therefore, the circuit board is more easily bent during welding. The tray provides maximum protection of the circuit board during soldering and prevents bending.

Similarly, in the automotive and consumer electronics industries, many special-shaped circuit boards have emerged for the needs of applications. It is sometimes difficult to transport these shaped plates with conventional chain rails and mesh belts, and placing the circuit board plates in trays allows any type of circuit board to be shipped.

By soldering some of the bottom components through the tray, it is also possible to use PCB wave soldering equipment for selective soldering of the product.

Since most trays are thick (sometimes 15 mm), solder certainly does not flow to the top of the board. The oxide layer on the solder surface will also be washed away by the edge of the tray before the board reaches the peak, so that when the solder starts, the tin is relatively clean.

By adding some stiffening strips to the tray, it can increase its hardness to withstand high-strength welding. It is also possible to install heat-absorbing blocks, component fixing devices and some other auxiliary devices on the upper part.

The use of pallets also helps standardize the width of the product line, soldering different circuit boards on the same production line, and can use bar code readers and other identification tools to quickly change process programs for different boards.

Although there are many advantages to using trays in lead-free soldering, it can also cause solder balls.

Requirements for pallet materials:
In order to maximize the service life of the trays, the trays must be made of materials that can withstand high temperatures and harsh process conditions, especially for lead-free soldering.

To meet these requirements, the material used to make the tray must meet the following characteristics:
• High dimensional stability
• Good thermal shock resistance
• Can remain flat after repeated use
• Corrosion resistance (flux and cleaning agent)
• Does not absorb moisture

The use of the tray brings the process problems:
The flux system must be able to spray the circuit board completely with flux. Poor tray designs can lead to “shadow effects” in flux spraying: Some parts of the board have insufficient flux or no flux at all. The flux must be sprayed onto the board and spread through the capillary action.

Before the tray touches the crest, it must be heated in the preheating unit. A typical preheating configuration is a combination of heat pipes and hot air forced convection. If the temperature drops before contact with the peak, the tray will have an endothermic effect, making the welding process difficult to control.

The use of trays requires a wave height of up to 0.5 inches (12.5 mm). In the case of such a high pump speed, the use of nitrogen can help reduce dross. When using pallets in lead-free soldering, Vitronics Soltec’s perturbed “smart wave” can also promote tinning of the perforated component.

In addition, we must pay special attention to keeping the circuit board in the pallet flat. If there is a gap between the circuit board and the tray, the flux will flow into the gap, and the solder will flow to the board when passing through the peak. This will cause solder residue on the board.

The gap between the circuit board and the tray may cause solder residue on the circuit board

Circuit board and tray design recommendations:
Avoid placing larger components near the piercing element as this can cause shadowing effects and tin difficulties.

Leave proper clearance around the pins and edges of the through-hole components so that solder can flow. These tin guides will guide the solder to the seat of the tray opening, while also greatly improving the solder flowability.

The tin slot at the tail of the tray allows the solder to flow smoothly back to the tin tank

The opening of the tray should be as large as possible to facilitate the flow of solder. This will reduce some of the welding defects, such as: short circuit and solder balls. At the same time, it is also beneficial to the solder filling of the through hole, because the large opening also means that there is more energy to enter the welding area.

1, using the next vacuum mode, in line with the theory of free fall, good dust collection effect.

2, special jig fixed more solid, to avoid the poor positioning caused by the cutting accuracy error.

3, the system automatically fixes according to the product installation location, to ensure high-precision product cutting requirements.

4, the static eliminator is installed in addition to electricity, dust blower continued to work to eliminate static electricity generated when cutting high-speed spindle to avoid damage caused by static electricity parts to avoid accumulation of dust due to static electricity.

IPC, Windows 7Program Backup程式备份USBSoftware access control软件权限管理密码保护，依权限进入对应操作界面，保护系统重要参数。(Password protection，the operator enter corresponding interface according to authority to protect important parameters.)Programming编程可视化界面，单个程序切割点容量无限制，切割路径动态模拟。(Visual interface, the cutting point capacity for a single program should be over 400, dynamic simulation of cutting schedule.)Auto correction of the mark pointMark点自动校准功能具备Mark点自动校准功能(Yes)Fixture 治具万用治具可供选择(universal fixture)Voice control噪音控制运行时，噪声小于60分贝（离设备一米距离测量）

1 years or more, spindle for 2 years or spindle maintenance service for 3000 hours.Technology Support技术支持及培训提供设备操作、编程，硬件保养，维修培训服务；程序永久免费升级。(Offer service of operation, programming, hardware caring and maintenance training; free upgrade of application. )

5.It is equipped with static eliminator. When dividing, the dust remover will work continuously to eliminate the static electricity generated when the high-speed spindle cut. It can avoid the damage caused by the static electricity and avoid the accumulation of dust due to static electricity.

PIC、Windows 7 or more advanced versionProgram Backup程式备份USBSoftware access control软件权限管理密码保护，依权限进入对应操作界面，保护系统重要参数。(Password protection，the operator enter corresponding interface according to authority to protect important parameters.)Programming编程可视化界面，单个程序切割点容量无限制，切割路径动态模拟。(Visual interface, the cutting point capacity for a single program should be over 400, dynamic simulation of cutting schedule.)Auto correction of the mark pointMark点自动校准功能具备Mark点自动校准功能(Yes)Fixture 治具ASC-3500S专用治具ASC-3500S special fixtureVoice control噪音控制运行时，噪声小于60分贝（离设备一米距离测量）

Over 1 year for the whole machine, and over 2 years for the spindle, and the spindle enjoys 3000 hours’ maintenance during the periodTechnology Support技术支持及培训提供设备操作、编程，硬件保养，维修培训服务；程序永久免费升级。(Offer service of operation, programming, hardware caring and maintenance training; free upgrade of application. )

10, the distance between the knife can be accurately adjusted, sub-board thickness to be met: 0.6MM-3.5MM up and down the distance between the knife can be accurately adjusted, sub-board thickness to be met: 0.6MM-3.5MM

11, the knife and the knife gap can be adjusted according to the PCB board V-CUT spacing, precision control in the 0.1MM

12, the distance between two adjacent blades can be adjusted between 8MM-25MM, can quickly adjust the required width;

13, circuit board material: aluminum, copper, FR4, glass fiber board;

14, Conveyor line speed can be adjusted;

15, the product pick and place institutions can be adjusted according to the width of the product;